This invention is generally directed to the treatment of patients with heart failure and specifically relates to cardiac assist devices and systems and the use thereof for such treatments.
Heart failure as a result of end stage coronary artery disease, or other cardiac conditions, is an increasingly prevalent problem. The costs associated with frequent hospital admissions, medications, and outpatient visits are staggering, and is estimated at almost $30 billion per year for the United States alone. Heart failure currently accounts for 6.5 million hospital days annually in the United States, 12-15 million office visits, and is the most frequent primary diagnosis for hospitalization. There are approximately five million people diagnosed with heart failure in the United States, and with an increasingly aging population, the absolute number of patients is increasing with about 550,000 people being newly diagnosed each year. It is estimated that as people approach 65 years of age, the number of people with heart failure is 10 per 1000 in the population. Despite advances in both diagnostic methods and treatment alternatives, the mortality for late stage heart failure, in symptomatic patients, approaches 50% at one year. For those with mild disease, the mortality rate is 50% within 4-5 years.
The heart failure is defined as a complex clinical syndrome that can result from any structural or functional cardiac disorder that impairs the ventricular filling and/or ejection of blood to the body. Manifestations of heart failure include dyspnea, fatigue, exercise intolerance, and fluid retention. Heart failure can also lead to pulmonary congestion and peripheral edema. Usually systolic and diastolic dysfunction co-exist. Neuro-hormonal factors may be altered and hemodynamic stresses increased. In late stage heart failure Left Ventricular (LV) filling pressures are increased and the QRS of the electrocardiogram may be widened. In addition, there may be refractory volume overload, decreased peak oxygen uptake with exercise, decreased cardiac output, narrow pulse pressure, tachycardia at rest, cool extremities, renal dysfunction, and altered mentation.
The causes of heart failure are many, the diagnosis is complex, but the fundamental hemodynamics are the same. There is an imbalance between cardiac output and the needs of the body. The imbalance of blood flow is associated with water retention resulting in central and peripheral edema. Moreover, a failing heart undergoes structural changes from the normal elliptical shape, namely, the heart dilates, and assumes a spherical shape. The ability to maintain adequate cardiac output is reduced. The degree of severity in reduced ejection fraction varies depending on how severe the heart failure is. As a result of spatial changes, the heart valves can become incompetent. The normal elasticity of the heart muscle is reduced or lost. The changes also lead to instability of the normal electrical function of the heart.
The American College of Cardiology and American Heart Association classified heart failure in four main categories, stage A and B are patients at risk or predisposed to failure, stage C is patients with current or past symptoms, and in stage D the patients have truly refractory or late stage failure. The treatment for heart failure is continually evolving. Patients in stages A, B, and C can usually be managed with effective pharmacological treatment and/or treatment of symptoms. Stage D patients may be eligible for specialized or advanced treatments which can include mechanical support, fluid removal, continuous inotropic support, cardiac transplantation, or innovative and experimental procedures.
Cardiac support devices monitor ventricular filling pressures and hemodynamic variables. They are designed to optimize LV filling pressures. In theory the devices alter physical stresses on the LV, and perhaps improve performance, and may prevent further ventricular dilation. Wrapping devices allow muscle shortening and resist circumferential expansion beyond the limits of the wrap. They serve as a constraining factor and give support to the heart.
Goals when implanting devices include improved blood flow, restoration of geometric and functional LV function, reshaping, and restoration of anteroapical and septal regions. Additional goals include enhancing the ability to generate force and muscle shortening, improve systolic and diastolic function, and to manage physiological factors of blood pressure, heart rate, blood volume, reduce ischemia, and to reduce filling pressures both at rest and with exertion.
At present, cardiac transplantation is the only established surgical treatment for end stage heart disease and cardiac failure. However, transplantation is available to less than 2500 patients in the US annually, a small fraction of patients with diagnosed end stage disease is considered. An innovative device designed to help refractory patients is needed.
Heart failure as a result of end stage heart coronary artery disease, or other cardiac conditions, is extremely prevalent, and the incidence is increasing annually. The costs associated with frequent hospital admissions, medications, outpatient visits, and other interventions are staggering. A method to ameliorate and/or reduce individual disability and the associated financial burden would benefit both the patients and society in general.
At the present time, heart failure accounts for more than 1 (one) million hospitalizations annually in the United States. More than 5 million people have a diagnosis of heart failure in the country, and with an increasingly aging population the absolute number of patients is increasing progressively.
Despite advances in diagnostic methods and treatment alternatives, the mortality of late stage disease, in symptomatic patients is estimated to be 50% at one year. For those with less severe disease the mortality is 50% within 4-5 years.
The causes of heart failure vary, depending on the underlying cardiac condition, but the fundamental defect is the same, an imbalance of blood supply from the heart to meet bodily demands. A failing heart undergoes structural changes, dilates, and assumes a spherical rather than elliptical shape. As a result of spatial changes the heart valves sometimes become incompetent. Spherical shapes lead to cardiac dysfunction, the mechanically efficient and electrically stable elliptical shape is lost.
A failing heart also suffers from a loss of elasticity, which means the pumping function to meet the needs of the body is inefficient or lost. Although a number of invasive procedures have been employed to remedy this condition, and new more effective medications have been developed, a fully satisfactory method of treating this very complex condition is not available.
Conventional approaches to the treatment of end stage disease and heart failure include medical treatment, interventions such as intra-aortic balloon pump, heart transplantation, and excision of non-contractile cardiac muscle. Experimental procedures include cardiomyoplasty and wrapping and supporting the heart.
Medical Treatment
The duration of effectiveness of medication varies, and often major side effects occur. Medication is a choice for Stages A and B heart failure, and can contribute to alleviating symptoms in stage C. In stage D, severe failure, medications are ineffective. There are no medications to force the myocardium with no contractile strength to perform effectively.
Intra-Aortic Balloon Counterpulsation
Intra-aortic Balloon Counter-Pulsation (IABP) is only effective on a very limited and temporary basis. It is not intended for long term use. Inflation and deflation of the balloon, which is usually inserted into the aorta percutaneously through the femoral artery, increases blood flow to the coronary arteries. In general, an increase of 10-20% in contractile function can be achieved. Morbidity increases with each day the balloon is in place, and includes obstructed blood flow to the affected limb, coagulopathy, infection, and malfunction of the inflation-deflation functions of the balloon.
Heart Transplantation
Heart transplant, as an option, is limited by the number of donor hearts available, and by the age and co-morbidity of the recipient. Following transplant, life long immune suppression therapy is required. Frequent medical follow-up is necessary, to evaluate effectiveness of immunosuppressive therapy and to monitor overall progress. The cost of medication and follow-up is high. Transplant rejection is always a consideration. Arteriosclerotic coronary artery disease in the transplanted heart is known to occur, and affects long term results.
Batista Procedure
In the Batista Procedure non-contractile muscle of the left ventricle is excised in order to increase cardiac output. The procedure is controversial, and the results are open to debate.
Cardiomyoplasty
Cardiomyoplasty involves an extensive surgical procedure. The latissimus dorsi muscle is dissected, lifted, and wrapped around the heart. Electrical stimulation of the implanted muscle results in muscle contraction, creating pressure on the ventricle, thereby increasing cardiac output. Because of the complexity and extent of the procedure it is only suitable for the most severe cases of heart failure. Pacemakers required for electrical stimulation of the muscle are costly. Extensive follow-up and care following the procedure is required.
Artificial Heart
A suitable artificial heart has yet to be developed, in spite of years of experimentation with varying models. One of the biggest obstacles is the incompatibility of the blood to device interface. The interface causes coagulation disturbances. External systems required to support the device and pumping mechanisms, are tethered to wall outlets, are large, and limit patient activity. There is high morbidity associated with the total artificial heart. Temporary assist devices, designed for use until a suitable donor heart can be found for permanent transplant, have many of the same drawbacks as the artificial heart.
Binding or Wrapping the Heart
A number of mechanical devices for increasing cardiac output and assisting the failing heart consist of a means such as wraps to compress the epicardial surface of the patient's myocardium. Various models and designs of cardiac wraps have been proposed, including wrapping the heart with a mesh or biocompatible material. Some cardiac wraps are inflatable so they can be inflated and deflated cyclically in response to cardiac parameters, In essence the principle of most wrapping devices is similar, to affect LV systolic pressure. In failure the end-diastolic pressure-volume (EDPVR) is altered. Right ventricular (RV) diastolic function is impaired. Wrapping does not increase diastolic function. Unfortunately, many binding or wrapping techniques do not consider septal motion, ventricular wall motion, chamber dynamics, and overall cardiac function.
Dynamic mechanical heart assist devices consist of wrapping the heart with two layers rather than one. The inner layer conforms to the epicardial surface of the heart throughout systole and diastole by means of a mechanical control system that inflates and deflates the inner wrap. The dynamic method provides enhanced support to the failing heart by closer regulation of cardiac function. The liner allows compression and relaxation of the cardiac muscle. The two layer device usually requires tubes, connected to the compression mechanism, to extend externally, outside the body, to access ports. Management of cardiac parameters is achieved mechanically by increasing or decreasing the amount of fluid in the liner. To acquire full knowledge of hemodynamics, direct pressure readings, echocardiographic evaluation, and other expensive and time consuming diagnostic tools are required.